The broad objective of this proposal is to acquire recombinant DNA molecules for genes specifically expressed as mature messenger RNAs in endodermal cells (and not expressed in embryonal carcinoma cells from which the endodermal cells were derived). The embryonal carcinoma lines to be examined are PSA-1 and F-9; the endodermal cell line to be examined is PF HR-9. The specific plan will involve a known endodermal gene product (laminin) and unknown endodermal specific genes. This will include: 1) examining the expression of laminin during PSA-1 differentiation to embryoid bodies and F-9 differentiation after admininstration of retinoic acid by radioactively labelling cells and immune precipitating the laminin; 2) the isolation of messenger RNA(s) enriched for laminin messenger RNA; 3) the screening of a mouse sperm DNA recombinant library with a complementary DNA to obtain recombinant molecules containing the laminin genes; 4) the use of the recombinant molecules to examine the transcriptional pattern of the genes during F-9 and PSA-1 differentiation to cells expressing laminin; 5) the synthesis of cDNA to endodermal mRNA; 6) the selection from this cDNA of sequences not expressed as mRNA in embryonal carcinoma cells; 7) the screening with this selected cDNA of a mouse sperm DNA recombinant library for recombinant molecules; 8) examining the level at which these genes are regulated during PSA-1 and F-9 differentiation to endoderm.